The proposed research will examine differential patterns of electrodermal and cardiac reactivity among conduct-disordered (CD), attention deficit hyperactivity-disordered (ADHD), and control groups of adolescents. Research by Fowles (1980, 1988) and others suggests that electrodermal reactivity during extinction, and heart rate reactivity during reward, represent the functioning of Gray's (1982a, 1982b, 1987a, 1987b) behavioral inhibition (BIS and behavioral activation (BAS) systems, respectively. According to this model, the disinhibition characteristic of both CD and ADHD results from an underactive BIS, an overactive BAS, or both. While deficits in electrodermal reactivity have been demonstrated in both CD and ADHD samples, heart rate is a contaminated measure of the sympathetically-mediated BAS, because it is also determined by parasympathetic input. This is particularly problematic given recent reports of deficits in parasympathetic functioning in CD samples. In the proposed research, electrodermal activity and appropriate measures of both sympathetic (pre-ejection period) and parasympathetic (vagal tone) influences on cardiac functioning will be assessed during reward, extinction, and passive coping. The pattern of results yielded is expected to provide an increment in specificity over Gray's model, with ADHD group exhibiting deficits in sympathetic functioning, and the CD group exhibiting deficits in both sympathetic and parasympathetic functioning compared to controls. This pattern would suggest a modification of Gray's model toward accounting for the aggression that accompanies behavioral disinhibition on CD but not ADHD samples.